1. Field of the Invention
The present invention relates to an optical disc reproduction apparatus for reading video, audio, and other information recorded on an optical disc such as a DVD (digital versatile disc) for the purpose of reproducing audio and video. More particularly, the present invention relates to an optical disc reproduction apparatus furnished with no capability of outputting DTS (digital theater system) audio on an analog basis but a capability of outputting it on a digital basis.
2. Description of Related Art
Among optical discs such as DVDs, those having recorded thereon various types of compressed audio data compatible with LPCM (linear pulse code modulation), Dolby digital, MPEG (Moving Picture Coding Experts Group) audio, DTS, etc. have conventionally been known as multiple audio stream optical discs. The current trend with such optical discs is that an increasing number of them have DTS audio recorded as the first stream.
On the other hand, among optical disc reproduction apparatus for reproducing audio and other information recorded on optical discs, some are not equipped with a decoder (a DTS recorder) for analog reproduction of DTS audio within an audio decoder for reproducing audio and are thus furnished with no capability of outputting DTS audio on an analog basis but a capability of outputting it on a digital basis (as a bit stream), and some are so configured as not to output DTS audio because no license fees have been paid for patents related to a DTS decoder.
Incidentally, in an optical disc reproduction apparatus furnished with no capability of outputting DTS audio on an analog basis but a capability of outputting it on a digital basis as described above, if the first stream of audio (the audio assigned an audio number “1”) recorded on an optical disc is DTS audio, the DTS audio is reproduced unconditionally. However, since the optical disc reproduction apparatus is furnished with no capability of outputting DTS audio on an analog basis, it cannot output audio, and thus remains silent. Seeing that the optical disc reproduction apparatus remains silent, the user may come to mistakenly believe that it has broken down.
According to the prior-art technique disclosed in Japanese Patent Application Laid-open No. 2004-220693, in an optical disc reproduction apparatus equipped with no DTS decoder, when DTS audio is recorded on an optical disc, the DTS audio is forcibly excluded from selection during reproduction. This, however, makes it impossible, when the user wants the DTS audio outputted during initial setting (setup), to output the audio even on a digital basis (as a bit stream).
According to the prior-art technique disclosed in Japanese Patent Application Laid-open No. 2002-170330, a muting circuit is activated at the start of reproduction. If a bit pattern checker detects a DTS synch signal and a DTS header signal in a bit stream within a predetermined period, the reproduction mode of signal processing is changed to a DTS mode, and the muting by the muting circuit is cancelled. If the bit pattern checker does not detect a DTS synch signal and a DTS header signal in the bit stream within the predetermined period, the reproduction mode of signal processing is changed to a PCM mode, and the muting by the muting circuit is cancelled.
This prior-art technique, however, is not meant to prevent an optical disc reproduction apparatus from remaining silent in a case where it is furnished with no capability of outputting DTS audio on an analog basis but a capability of outputting it on a digital basis and it is so configured as to output DTS audio unconditionally when the first stream of audio (the audio assigned an audio number “1”) recorded on an optical disc is DTS audio.
According to the prior-art technique disclosed in Japanese Patent Application Laid-open No. 2002-251827, before the start of reproduction of a data stream recorded on a disc, silent digital audio in the same format as the digital audio that is about to be outputted is recorded in a memory in advance, and the silent digital audio is outputted to prompt quick decoding of the digital stream.
This prior-art technique, however, is also not meant to prevent an optical disc reproduction apparatus from remaining silent in a case where it is furnished with no capability of outputting DTS audio on an analog basis but a capability of outputting it on a digital basis and it is so configured as to output DTS audio unconditionally when the first stream of audio (the audio assigned an audio number “1”) recorded on an optical disc is DTS audio.
The prior-art technique disclosed in Japanese Patent Application Laid-open No. 2000-222826 relates to a D/A conversion device that converts a compressed digital audio signal and a non-compressed digital audio signal into an analog audio signal, and more particularly to a muting device that brings a signal amplifying circuit for amplifying an analog audio signal into a muting state when audio is silent during reproduction of both a compressed digital audio signal and a non-compressed digital audio signal. Thus, this prior-art technique does not relate to an optical disc reproduction apparatus furnished with no capability of outputting DTS audio on an analog basis but a capability of outputting it on a digital basis.